The invention relates to an advancing device with a fluid power piston and cylinder arrangement comprising a stationarily mounted cylinder whose two ends are closed by cylinder end caps, a piston arranged for motion in the longitudinal direction of the cylinder, a piston rod connected with the piston and extending sealingly through one of the end caps, a load driving member mounted on a section of the piston rod located outside the cylinder and adapted to perform a linear advancing motion on operation of the piston and cylinder arrangement, and a guide for guiding motion of the load.
Advancing devices of this type are used in the mechanical engineering field, as for example in a machine tool, to shift a workpiece into a desired position in which it is to be machined. In such a case the load drive member will be in the form of a machine carriage, which is mounted on the piston rod to form an axial extension thereof. The topside of the load driving member is designed as the carriage that it is able to carry the work. The opposite, lower side of the machine carriage runs in a guide, which simultaneously forms a plain bearing designed to carry the mass of the work. By suitable operation of the piston and cylinder arrangement, it is possible to move the work along in the longitudinal direction of the cylinder and to position it in any desired setting as required. Further possible applications of the above mentioned advancing device are conceivable, as for instance in which the load driving part is in the form of a plunger shaped to meet the requirements of a given case. All known advancing devices have the shortcoming that they are relatively long when measured in the direction of advance so that the machines equipped with them will also be relatively long. The long overall length is due to the placement of the piston and cylinder arrangement and the load driving part along a single axis, i.e. without overlap. This manner of construction furthermore involves a slow assembly of the advancing device which needs frequent adjustment. Since in fact the guide of the load driving member necessarily has to be mounted on the machine frame, exact adjustment of the advancing device is required in order to ensure satisfactory sliding of the load drive member on the guide. This obviously involves high assembly or fitting costs. Last but not least, the production of the guide for the load driving member is complex, and the fitting of the guide to suit the geometry of the load driving member and that of the machine tool to have with the advancing device is always a slow job. In fact, different types of machine require different designs of the guide. This is more particularly a disadvantage in the production of customized or special purpose machines, which are generally produced in one unit at a time with a unique design of the load driving member and the guide therefor.